True story: I was once working on a model (which eventually became a multi-million dollar business for the company, and has since been patented. The prototype work was being done partly in Excel.
While I was gone on vacation, my boss and co-workers were forced to give an update on this work to management and a key client. They had a bit of trouble running it … because a key parameter was located in cell AC8492.
It wasn’t intended to be there of course; the model just got built day by day and while it was in preliminary stages it was clear enough for ME to work on for several hours a day – but nearly impossible for anyone else to figure out then (or me to figure out now, should I need to go back to it.